ИСТИНА

The genus Paeonia L. with approximately 35 species of perennial herbs and shrubs is taxonomically isolated, having been placed in its own monotypic family (Paeoniaceae). However, species boundaries within the genus are obscured due to a great morphological variability and cases of reticulate evolution. Internal transcribed spacer (ITS) sequence additivity is usually used as evidence of the hybrid nature of species. The focus of the present study is on the nuclear ribosomal transcribed spacer (ITS and external transcribed spacer (ETS)) sequence diversity and species delineation in three groups of herbaceous species, namely, Paeonia obovata complex (P. obovata, and P. oreogeton) distributed in East Asia, Paeonia anomala complex (P. anomala, P. hybrida, and P. intermedia) from Central Asia, Siberia, and adjacent northeastern European regions, and P. lactiflora of Central and Eastern Asia. All were studied from several populations for investigation of infraspecific variation of sequences. The nucleotide sequences were obtained by direct Sanger sequencing of amplicons. The present study shows that all species groups are characterized by a large number of nucleotide positions exhibiting additive polymorphic sites. Nucleotide additivity occurs in the ITS and ETS sequences and characterizes the group of species as a whole (Paeonia obovata complex and P. intermedia + P. hybrida) or separate species (P. intermedia, P. hybrida, P. anomala, and P. lactiflora). A lot of additive nucleotides are not found in other species, which could be considered as parent forms. In many cases, the studied species are not characterized by nucleotide substitutions, but only by additive nucleotides. Different ITS/ETS types arise by means of nucleotide substitutions across the loci. The level of spacer variation is high if the rate of concerted evolution is lower than the mutation rate. It is possible that additive polymorphism observed in nuclear ribosomal transcribed spacers reflects not only hybrid origin of species but also a recent divergence of the group.